The invention relates generally to semiconductor lasers. More particularly, the invention relates to tuning the wavelength of output photons in optically pumped semiconductor lasers.
Semiconductor lasers have become more important. One of the most important applications of semiconductor lasers is in communication systems where fiber optic communication media is employed. With growth in electronic communication, communication speed has become more important in order to increase data bandwidth in electronic communication systems. Improved semiconductor lasers can play a vital roll in increasing data bandwidth in communication systems using fiber optic communication media such as local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs). A preferred component for optical interconnection of electronic components and systems via optical fibers is a semiconductor laser known as a vertical cavity surface emitting laser (VCSEL). The current state of design and operation of VCSELs is well known. Due to optical properties of optical fibers, photons emitted at longer wavelengths from a laser tend to propagate longer distances due to lower loss and smaller dispersion. Thus, forming a VCSEL that can operate at longer wavelengths, such as a wavelength greater than 1.25 xcexcm, is desirable.
Lasers can be excited or pumped in a number of ways. Typically, VCSELs have been electrically excited (electrically pumped) by a power supply in order to stimulate photon emission. However, achieving photon emission at long wavelengths using electrical pumping has not been commercially successful due to a number of disadvantages.
More recently it has been shown that a VCSEL can be optically excited (optically pumped) to stimulate photon emission. Referring now to FIG. 1, it has been shown that an in-plane laser 100 can have its emitted photons 101A redirected by a mirror 102 into the direction of photons 101B for coupling into a VCSEL 106. The in-plane laser 100 is designed to be electrically excited in order to emit photons 101A at relatively short wavelengths (850 nanometers (nm) to 980 nanometers (nm)). The redirected photons 101B from the in-plane laser 100 optically excite the VCSEL 106. The VCSEL 106 is designed to be optically excited in order to emit photons 108 at relatively long wavelengths (1250 nm to 1800 nm). A disadvantage to the system of FIG. 1 is that the wavelength for the photons emitted by the VCSEL 106 are not tunable. Typically, the long wavelength of the output photons is designed to a predetermined value by the materials selected in forming the VCSEL 106.
Wavelength tunable lasers are important for dense wavelength division multiplexed (DWDM) applications where a semiconductor laser wavelength has to comply with an International Telecommunications Union (ITU) wavelength grid. Using a distributed feedback (DFB) laser formed to generate photons near the wavelength of interest, a conventional method to fine-tune the wavelength of the laser is to control the laser operation temperature. In order to generate wavelengths of photons over the whole range of the ITU wavelength grid, many DFB lasers formed to generate different wavelengths can be used and multiplexed together. However, due to the large number of lasers involved, the system complexity is rather high and stocking the entire range of lasers for replacement is bothersome.
Another means to tune the wavelength of a DFB laser is to use sampled grating technology. One problem associated with using sampled grating technology is that device yields can be low due to the grating complexity. Additionally, the control electronics for tuning the wavelength of a DFB laser using sampled grating technology can be complicated. Additionally, the coupling efficiency of the photons generated by DFB lasers into a single mode fiber is typically low due to a spatial mismatch between the DFB""s output laser beam and the fiber core of a single mode optical fiber.
Because long wavelength VCSELs can have a circular beam profile, the coupling efficiency into an optical fiber can be superior to a DFB laser. Thus if the wavelength of photons output by a long wavelength VCSEL can be tuned, greater advantages can be achieved over that of a tunable DFB laser.
One way that a long wavelength VCSEL may be tunable is through the application of Microelectromechanical Systems (MEMS) film technology. MEMS film technology involves forming an MEMS film directly onto the VCSEL. One drawback to using MEMS technology is that MEMS film is rather fragile and may be destroyed. Additionally, MEMS film is sensitive to mechanical vibrations and vibrations induced by noise. Furthermore, yields of devices incorporating MEMS technology are typically low.
It is desirable to overcome the limitations of the prior art.